Many of us have heard the phrase “the rest of the story” used as a preface to additional facts that sometimes do not make it into a story as widely published. But once the additional information is explained, we learn that we do not always get all the important information the first time around.
What brings this up was an item in an RV magazine I stumbled upon when cleaning out some old boxes of stuff. This is from November 2008, but the facts and information are still important today. The author is one of that small group of RV “experts” that make a living providing information on the Internet on just about all things RV. Sometimes they are answering questions about refrigerators, then they might be answering a question on holding tanks or plumbing. From my point of view, it seems that they are quite knowledgeable about most topics. But sometimes there are important details related to tires that don’t always make it into their posts.
The owner of a 5th wheel trailer had purchased a set of tires and offered that the tire store inflated the tires to 85 psi, which was the “maximum” as molded onto the tire sidewall. The owner said he had heard that using the maximum inflation from the tire as the standard pressure was advisable. He wanted to know the “rule of thumb” for the proper inflation.
Reduce tire pressure for higher elevations?
He also wanted to know if he needed to reduce the tire pressure when he traveled to 8,000-foot elevations.
The “expert” correctly replied that the inflation on the tire was the minimum required to carry the load on the tire. He continued with the recommendation that tire loads be measured on a truck scale and then the inflation set based on Load & Inflation tables. There was no mention of ensuring that there was at least a 10% margin between the tire Load Capacity and the actual load on the tire. This recommendation to a trailer owner would address some of the unique side loading (Interply Shear) seen on multi-axle trailers – which is significantly different than that seen on motorized RVs.
I advocate that trailer owners get their rig weighed so they can confirm they are not overloading any individual tire, as it is not unusual for one tire or axle to be 500 to 1,000 pounds away from a theoretical 50/50 weight balance. I do strongly suggest that all multi-axle trailers run the inflation shown on the tire. In most cases, that is the inflation shown on the RV placard as provided by the RV manufacturer. This will help reduce the side force overload seen by trailers but not by motorhomes.
The expert did correctly advise that while the tire pressure will change with elevation, unless the owner was checking his inflation daily, “as recommended,” it was not necessary to adjust inflation when traveling to high elevations.
Importance of setting proper inflation
When I originally read this reply I was concerned, and did send a letter to the expert pointing out the missed opportunity to educate RV owners about the importance of setting proper inflation. I mentioned that a stronger statement on more frequent or constant inflation checks by using a tire pressure monitoring system (TPMS) was needed.
I do not consider daily inflation checks sufficient, especially for towables. Too often the driver of the tow vehicle has no idea a tire is losing air until it is too late to save the tire and there has been a “blowout” from a puncture or leaking valve. That could cause thousands of dollars worth of damage to the RV. I also would not imply that when traveling to high elevations it isn’t necessary to adjust your inflation whenever the inflation is checked.
As you can see, the general RV expert provided mostly correct information, but he left out some considerations that I, as a tire engineer, do believe to be very important.
Have a tire question? Ask Roger on his new RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
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Roger, are you recommending that on trailers the air pressure stamped on the sidewall should be the pressure to be running the tires at? Does the same apply to motorhomes?
I am recommending the trailer tires be inflated to the Certification Sticker number AND that you confirm the tire load is no more than 85% of the tire load capacity shown in the Load Inflation tables. For Motorhomes I am recommending that the load be no more than 90% of the load capacity found in the tables.